/Engine/Source/Runtime/Core/Public/Math/UnrealMathUtility.h
Determines whether a given set of points are coplanar, with a tolerance. Any three points or less are always coplanar.
Whether the points are relatively coplanar, based on the tolerance
static bool PointsAreCoplanar ( const [TArray](API\Runtime\Core\Containers\TArray)< FVector > & Points, const float Tolerance )